Showing papers by "Ali H. Sayed published in 2004"
TL;DR: This letter proposes two new variable step-size algorithms for normalized least mean square and affine projection that lead to faster convergence rate and lower misadjustment error.
Abstract: This letter proposes two new variable step-size algorithms for normalized least mean square and affine projection. The proposed schemes lead to faster convergence rate and lower misadjustment error.
529 citations
TL;DR: A unified treatment of the mean-square error, tracking, and transient performances of a family of affine projection algorithms based on energy conservation arguments and does not restrict the regressors to specific models or to a Gaussian distribution.
Abstract: Affine projection algorithms are useful adaptive filters whose main purpose is to speed the convergence of LMS-type filters. Most analytical results on affine projection algorithms assume special regression models or Gaussian regression data. The available analysis also treat different affine projection filters separately. This paper provides a unified treatment of the mean-square error, tracking, and transient performances of a family of affine projection algorithms. The treatment relies on energy conservation arguments and does not restrict the regressors to specific models or to a Gaussian distribution. Simulation results illustrate the analysis and the derived performance expressions.
318 citations
TL;DR: This note addresses the problem of robust multiobjective filtering for discrete time-delay systems with mixed stochastic and deterministic uncertainties, in addition to unmodeled nonlinearities.
Abstract: This note addresses the problem of robust multiobjective filtering for discrete time-delay systems with mixed stochastic and deterministic uncertainties, in addition to unmodeled nonlinearities. A procedure is developed for the design of linear and exponentially stable filters with a bounded error variance, exponential rate of decay, and robust performance for the error system.
54 citations
TL;DR: This note develops robust filters for time-varying uncertain discrete-time systems based on a data regularization solution and they enforce a minimum state-error variance property.
Abstract: This note develops robust filters for time-varying uncertain discrete-time systems. The developed filters are based on a data regularization solution and they enforce a minimum state-error variance property. Simulation results confirm their superior performance over other robust filter designs.
38 citations
17 May 2004
TL;DR: The effect of IQ imbalances on OFDM receivers is analyzed and system level algorithms to compensate for these distortions are proposed and include different post and pre-FFT estimation and correction techniques.
Abstract: OFDM is a widely recognized and standardized modulation scheme for future high bit rate communications. Implementation of OFDM-based systems suffers from inphase-quadrature phase (IQ) imbalances in the front-end analog processing. The IQ imbalances can severely limit the operating SNR and, consequently, the supported constellation sizes. In this paper, the effect of IQ imbalances on OFDM receivers is analyzed and system level algorithms to compensate for these distortions are proposed. The algorithms include different post and pre-FFT estimation and correction techniques.
32 citations
TL;DR: An adaptive filter is developed using the proposed criterion with essentially the same complexity as the standard least mean squared (LMS) algorithm and outperforms LMS specially in situations with fast channel variations.
Abstract: The mean-squared-error criterion is widely used in the literature. However, there are applications where the squared-error is not the primary parameter affecting the performance of a system. In many communication systems, for instance, the information bits are carried over the phase of the transmitted signal. In this letter, we introduce a cost function that is based on both the error magnitude and the phase error. The criterion is useful for applications where the performance depends primarily on the phase of the estimated (recovered) signal. An adaptive filter is then developed using the proposed criterion with essentially the same complexity as the standard least mean squared (LMS) algorithm. The filter outperforms LMS specially in situations with fast channel variations. Bit error rate (BER) simulations for two communication systems using the proposed algorithm support the claims.
30 citations
17 May 2004
TL;DR: A probabilistic routing algorithm for wireless ad-hoc networks that can tolerate end-to-end delays and those for which the final destination for the packets is a small region is proposed.
Abstract: We propose a probabilistic routing algorithm for wireless ad-hoc networks. The focus is on applications that can tolerate end-to-end delays and those for which the final destination for the packets is a small region. The nodes are assumed stationary and establish connections with a master node according to a priority scheme that relates to their distances from the master node. Simulation results illustrate the performance of the proposed algorithm.
8 citations
07 Nov 2004
TL;DR: An efficient beamforming scheme in terms of feedback rate is proposed in this article, which exploits the channel statistics by using space and time correlation in a joint manner in order to track the channel at the transmitter.
Abstract: With multiple antennas at the transmitter, either space-time block coding or beamforming can be used as the transmission scheme depending on the availability of channel state information at the transmitter. Although beamforming can provide superior performance over space-time block coding, it nevertheless suffers from feedback overhead. An efficient beamforming scheme in terms of feedback rate is proposed in this paper. The proposed scheme exploits the channel statistics by using space and time correlation in a joint manner in order to track the channel at the transmitter. Simulation results show improvements compared to a system with space-time block coding.
8 citations
18 Jul 2004
TL;DR: Significant performance improvement is achieved by using the proposed receiver compared to a standard receiver with no compensation for IQ imbalances, and an efficient receiver with compensation forIQ imbalance is then derived.
Abstract: Implementation of OFDM-based systems suffers from in-phase and quadrature-phase (IQ) imbalances in the front-end analog processing. The resulting distortion due to IQ imbalances can limit the achievable operating SNR at the receiver, especially when space-time coding is used for enhanced received SNR. In this paper, the effect of IQ imbalances on an OFDM-based system with Alamouti coding is studied and an efficient receiver with compensation for IQ imbalances is then derived. Significant performance improvement is achieved by using the proposed receiver compared to a standard receiver with no compensation for IQ imbalances.
6 citations
07 Nov 2004
TL;DR: In this paper, the mean-square performance of adaptive filters is studied in terms of stability conditions and expressions for the mean square error and mean square deviation of the filters, as well as the transient performance of the corresponding partially averaged systems.
Abstract: This paper uses averaging analysis to study the mean-square performance of adaptive filters, not only in terms of stability conditions but also in terms of expressions for the mean-square error and the mean-square deviation of the filters, as well as in terms of the transient performance of the corresponding partially averaged systems. The treatment relies on energy conservation arguments. Simulation results illustrate the analysis and the derived performance expressions.
6 citations
TL;DR: This paper illustrates the impact of In-phase and Quadrature-phase (IQ) imbalances on system performance and the structure of space-time block codes are exploited to design reduced-complexity adaptive receivers that are robust to IQ imbalance.
11 Jul 2004
TL;DR: An adaptive receiver for multiple-input multiple-output (MIMO) frequency selective channels that employ space-time block-coded transmissions with cyclic prefixing is developed.
Abstract: We develop an adaptive receiver for multiple-input multiple-output (MIMO) frequency selective channels that employ space-time block-coded transmissions with cyclic prefixing. The receiver performs both interference suppression and equalization for multiuser transmissions. The structure of the space-time code is exploited to show that the receiver can be implemented on a per-frequency-bin basis rather than on a block-by-block basis. The adaptation scheme requires solving N independent problems each of complexity O(M/sup 2/) per block iteration, where M is the number of users and N is the block size.
18 Jul 2004
TL;DR: A unified framework for adaptive channel estimation for multi-user Alamouti STBC transmissions over flat fading channels and over frequency selective fading channels using single-carrier frequency domain (SC-FD) STBC or STBC-OFDM is described.
Abstract: We develop adaptive channel estimation techniques for multiple-input multiple-output (MIMO) channels with space-time block-coded (STBC) communications. We describe a unified framework for adaptive channel estimation for multi-user Alamouti STBC transmissions over flat fading channels and over frequency selective fading channels using single-carrier frequency domain (SC-FD) STBC or STBC-OFDM. The structure of the space-time code is exploited to reduce the complexity of block NLMS and RLS receivers.
11 Jul 2004
TL;DR: An adaptive procedure is developed for AOA estimation under multipath and multiuser conditions and simulations illustrate how the adaptive solution improves location accuracy.
Abstract: Reliable positioning of CDMA cellular users in a mobile environment relies on accurate knowledge of the time-of-arrival (TOA) and angle-of-arrival (AOA) of the first arriving ray. An adaptive procedure is developed for AOA estimation under multipath and multiuser conditions. Simulations illustrate how the adaptive solution improves location accuracy.
17 May 2004
TL;DR: Simulation results illustrate the performance of the proposed strategies for bandwidth allocation with soft and hard constraints, as well as power allocation strategies for a class of wireless networks with a clustering protocol.
Abstract: In this paper, we propose resource allocation strategies for a class of wireless networks with a clustering protocol. The nodes are assumed stationary and establish connections with the master node according to a priority scheme that relates to their distances from the master node. The paper considers bandwidth allocation with soft and hard constraints, as well as power allocation strategies. Simulation results illustrate the performance of the proposed strategies.
11 Jul 2004
TL;DR: The authors derive performance expressions for the throughput and blocking probability for a class of wireless networks with a clustering protocol that is assumed stationary and establishes connections with the master node according to a priority scheme that relates to their distances from the master nodes.
Abstract: We derive performance expressions for the throughput and blocking probability for a class of wireless networks with a clustering protocol. The nodes are assumed stationary and establish connections with the master node according to a priority scheme that relates to their distances from the master node. The latter is selected randomly in a cell and data are transmitted within predefined sectors.
Proceedings Article•
01 Jan 2004
TL;DR: This paper designs a regularized robust filters for state-delayed systems that perform regularization as opposed to deregularization and allows for stochastic uncertainties in the state matrices and deterministic uncertainties for the output matrices.
Abstract: The Kalman filter is the optimal linear least-mean-squares estimator for systems that are described by linear state-space Markovian models [1]. However, when the model is not accurately known, the performance of the filter can deteriorate appreciably. There have been many approaches to robust filtering in the literature (see, e.g., [2]). In [3, 4], frameworks for robust filter designs were discussed that perform regularization as opposed to deregularization. In this paper, we pursue the design of such regularized robust filters for state-delayed systems. We also allow for stochastic uncertainties in the state matrices and deterministic uncertainties for the output matrices and design a robust filter that bounds the state error covariance matrix. Thus consider an n−dimensional state-space model of the form
01 Jan 2004
TL;DR: A robust algorithm is developed for jointly controlling the power and rate of flow in a distributed wireless network as a discrete-time state-delayed system with uncertainties and achieves better SIR performance than a conventional power control scheme.
Abstract: A robust algorithm is developed for jointly controlling the power and rate of flow in a distributed wireless network. The dynamics of the network is modelled as a discrete-time state-delayed system with uncertainties and the proposed algorithm achieves better SIR performance than a conventional power control scheme. keywords: Robust estimation, congestion control, power control, rate control, wireless network, convex optimization.
TL;DR: Adapt channel estimation techniques for space–time block–coded (STBC) multiple–input multiple–output (MIMO) orthogonal frequency division multiplexing (OFDM) communications are developed.
17 May 2004
TL;DR: A receiver design for joint interference suppression and equalization of asynchronous multi-user space-time block coded (STBC) systems and the design of front end prefilters to synchronize the received blocks from all users is described.
Abstract: We present a receiver design for joint interference suppression and equalization of asynchronous multi-user space-time block coded (STBC) systems. We describe the design of front end prefilters to synchronize the received blocks from all users. Simulation results show significant performance improvement for asynchronous transmissions.
Proceedings Article•
01 Sep 2004
TL;DR: The MMSE channel estimator for multi-user Alamouti STBC transmissions over both flat fading and frequency selective fading channels is derived from the structure of the space-time code to reduce the complexity of the algorithm.
Abstract: We develop channel estimation techniques for multiple-input multiple-output (MIMO) channels that employ space-time block-coded (STBC) transmissions. We derive the MMSE channel estimator for multi-user Alamouti STBC transmissions over both flat fading and frequency selective fading channels. The derivation exploits the structure of the space-time code to reduce the complexity of the algorithm.
27 Jun 2004
TL;DR: The paper considers bandwidth and rate allocation for a class of wireless networks with a clustering protocol that is assumed stationary and establishes connections with the master nodes according to a priority scheme that relates to their distances from the master node.
Abstract: We propose resource allocation strategies for a class of wireless networks with a clustering protocol. The nodes are assumed stationary and establish connections with the master node according to a priority scheme that relates to their distances from the master node. The paper considers bandwidth and rate allocation.